My sister always wakes up early. She has to be at school by 7:00.
What is the best way to combine these sentences?

A:My sister always wakes up early; she has to be at school by 7:00.
B:My sister always wakes up early; because she has to be at school by 7:00.
C:She has to be at school by 7:00, instead, my sister always wakes up early.
D:She has to be at school by 7:00, then my sister always wakes up early.